Iran is home to some of the world's largest oil and gas reserves but U.S. energy firms have been barred by Washington from Iran for nearly two decades.
Several European oil and gas companies had planned multi-billion dollar investments over the last decade to help develop Iranian reserves.
However U.S. pressure drove European energy companies away from Iran in the late 2000s, for fear of jeopardizing their interests in the U.S. market if they stayed.
Western companies, whose technology Tehran needs to fully exploit its oil and gas riches, are keen to go back into Iran when sanctions are lifted.
Despite the landmark deal struck on Sunday, U.S. restrictions on trade, including those banning long-term investment or provision of technical services to Iran's energy sector, are still in place.
Sanctions preventing the sale of petroleum products to Iran, which needs to import such fuels because it lacks refining capacity, also remain in effect.
Potential buyers of Iranian crude have found it difficult to insure their multi-million dollar shipments, because of wide-ranging restrictions on providing financial services for Iranian trade.
The White House fact sheet says that financial sector sanctions remain intact, along with those affecting Iranian shipping companies.
However, a senior western official said on Sunday that relief on EU sanctions on oil shipping insurance was included in the deal.
The EU could relax insurance restrictions without causing a rebound in Iranian oil exports by only allowing customers to insure their current volume of oil purchases and no more. It is unclear how the EU would police this.